The inventive concept relates to image sensors.
An image sensor may employ a semiconductor device for converting an optical image into an electrical signal. Image sensors that employ semiconductor devices include charge coupled devices (CCD) and CMOS image sensors (CIS). CCDs are used in video cameras and CIS are used in digital still cameras.
A CIS includes a plurality of pixels. Each pixel, in turn, includes a photodiode (PD) for sensing incident light and transistors for transferring signals produced by the photodiode to a signal processing circuit.